(1) Field of the Invention
The present invention relates to testing tubular materials and structures, and more particularly the seams or joints thereof which are tested under mechanical load comparable to service conditions.
(2) Description of the Prior Art
In the previous practice of testing butt welds, lap welds, and the like, at room temperature, a tubular specimen was mounted with one end secured rigidly in a suitable frame with the weld or seam to be tested adjacent a movable series of loose spherical balls or spheres adapted to contact the seam area. The spheres were only temporarily retained in sockets on a mandrel, and following considerable mechanical loading, tended to separate from the mandrel with great force upon breakage of the weld or seam area. In this practice, the series of spheres are moved simultaneously on and with the mandrel to place internal loading on the weld or seam area. As stated, upon breakage, such spheres tend to fly at random with explosive force creating a potential serious injury hazard. Shielding of such testing apparatus is normally required.
Another type of previous practice of testing welds, especially at elevated temperature and pressure, consisted of mounting the tubular specimen rigidly in a stationary frame in a manner such that the weld or seam to be tested was adjacent a fixed support. The opposite end of the specimen was then subjected to a bearing force of cyclical nature, normally in one plane of motion. Partial tests of tube welds were performed in this manner. However, the flexing action thus applied did not stress all portions of the weld accurately and did not reproduce service conditions of temperature and pressure simultaneously. Therefore, such weld tests previously made have been inadequate in determining the suitability of certain weld types for prescribed service usage.
Another type of apparatus for testing tube welds consists of a test stand for subjecting a tubular specimen to fatigue tests under repeated stressing of known loading amounts with the forces equally distributed on all sides of the cylindrical shape. This apparatus is adapted to duplicating in the tube welds similar severe conditions of temperature and pressure. Such apparatus is disclosed in U.S. Pat. No. 2,761,310 to Siegel, issued Sept. 4, 1956.
A still further type of device for weld testing is disclosed in U.S. Pat. No. 3,500,679 to Smith, issued Mar. 17, 1970. This device provides a test stand for bending the welded specimen into a substantially U-shape with anti-friction elements to assist in such bending.
The following additional patents pertain to testing welds in metals by various methods:
U.S. Pat. Nos. 1,200,086; 1,925,718; 2,002,552; 2,742,782; 2,776,695; 3,410,133; 3,636,758; 4,107,979.